Air intake arrangement for air jacketed combustion chambers



Feb. 13, 1951 M. A. MAYERS ET AL AIR INTAKE ARRANGEMENT FOR AIR JACKETEDCOMBUSTI ON CHAMBERS Sheets-Sheet l Filed July 8, 1946 INVENTORS. Martinfl. Mayers Hans Th olzwarth Patented Feb. 13, 1951 AIR INTAKEARRANGEMENT FOR AIR JACKETED COMBUSTION CHAMBERS Martin A. Mayers,Maplewood, and Hans T. Holzwarth, Westfield, N. J., assignors to The M.W. Kellogg Company, New York, N. Y., a

corporation of Delaware Application July 8, 1946, Serial No. 681,954

18 Claims. 1

The present invention relates to combustion units and methods of thegeneral character in which fuel is injected into a chamber or furnaceand burned in the presence of air, and although it has a wide range ofutility, it is particularly useful, for example, in connection with gasturbine plants.

One object of the present invention is to provide a new and improvedcombustion unit of the general type referred to, and a new and improvedmethod of combustion.

Another object of the present invention is to provide a new and improvedcombustion unit of the general type referred to, in which the combustionair inlet and the exhaust outlet are designed and located to permit thecompact arrangement of said combustion unit in line with other units ofa plant, while afiording high combustion rates and low pressure drops. Acombustion unit of this improved type is particularly useful inconnection with certain proposed aircraft practices in which theprincipal elements of a gas turbine plant, as for example, thecompressor, combustion unit and gas turbine are arranged in line.

A further object of the present invention is to provide a new andimproved combustion unit, which affords high combustion rates and lowpres sure drops, and which at the same time, is designed to divert partof the inlet air stream for effective cooling of the unit walls with aminimum of adverse effect on the eflicient thorough mixing of the fueland air in the interior of the combustion chamber.

A further object of the present invention is to provide a new andimproved combustion unit,

which is designed to assure thorough and rapid mixing of the air andfuel in accordance with substantially predetermined flow patterns, andwhich therefore lends itself to stabilized operation' and to effectiveeasy and close regulation.

In carrying out certain features of the present invention, fuel iscontinuously injected into the front end of a combustion chamber definedby an inner wall" desirably in the form of a shell disposed within ahousing. The wall of the housing is spaced from the wall of the innershell to form therewith an annular space for the air cooling of thehousing wall. A combustion air duct has its inlet located near the frontof the unit with its line of flow substantially parallel to thelongitudinal axis of the unit, and its outlet connecting into thehousing wall. The inner shell has an air inlet opening in its peripheralwall opposite the outlet of the air duct, so that the major part of theair from said air duct is delivered into the interior of the inner shellfor secondary combustion in its burning out zone. Part of the air fromthe air duct is diverted through vaned openings in the inner shell forprimary combustion in the ignition zone, part of it is diverted aroundsaid shell and towards the front end of the combustion unit for coolingthe ignition zone section of the inner shell wall, the housing walland'the fuel injection nozzle, and part of it is diverted towards therear or outlet end of the unit and into an annular cooling spacesurrounding the inner shell to air-cool the housing wall.

The air duct is designed so that although it extends longitudinally inthe same general direction as the combustion chamber, it delivers an airstream at proper pressure into the interior of the housing substantiallyat right angles to the longitudinal axis of the combustion chamber. Thepart of the air stream which projects into the interior of thecombustion chamber through its peripheral inlet opening is directed bythe peripheral wall of said combustion chamber into two similaradjoining vortex streams having opposite senses of rotation, and havingtheir axes running substantially parallel to each other along thechamber.

The primary air diverted towards the ignition zone is thoroughly mixedtherein with the fuel injected into said zone, and forms with said fuelan inflammable mixture rich with fuel. This mixture is ignited and theresulting products at ignition temperature projected into the secondarycombustion chamber. The injected fuel elements which are not burnt andthe products of combustion from said zone tend to be drawn into andalong the respective axes of the two reverse air vortices created in thecombustion chamber, and form an intimate mixture with the vorticallycirculated air, thereby effecting rapid intense combustion of thefuel-air mixture progressively along the combustion chamber.

Unless the conditions are right, the two reverse air vortices will notmaintain their substantially predetermined flow characteristics and willbecome unstable. Unstable operation is generally accompanied by longflames and ineffective combustion. Also. under unstable operating flowconditions described, oil drops may be thrown against the inside of theinner shell with an accompanying tendency to produce coke and high walltemperatures. By maintaining the two air vortices of substantiallyuniform diameter and shape throughout their lengths, the length ofcombustion flame will be maintained at a minimum, and a more stabilizedflame condition is attained, permitting thereby easy close control ofthe unit.

It has been found in accordance with the present invention, that for anygiven form and size of inlet opening in the inner shell or combustionchamber, only a limited portion of the total air supplied may bepermitted to flow into the cooling annular flow space around saidcombustion chamber without adversely affecting the stability of thedouble vortex flow in said chamber. If a greater amount than thisproportional limit is permitted to flow into this annular space, thedouble vortex system becomes unstable.

It has furthermore been found in accordance with the present invention,that the shape of the air inlet opening in the inner shell or combustionchamber has an influence on the stability of the double vortex flowpattern in said chamber. It has been found that the air inlet openingmost desirable from the standpoint of bivortical flow stability in thecombustion chamber should be, or approach, a rectangle, with two sidesextending substantially parallel to the longitudinal axis of thechamber, and should have its measure lengthwise of the chamber nogreater than its transverse chordal dimension. A transverse opening orslit having its transverse chordal dimension at right angles to thelongitudinal axis of the combustion chamber greater than itslongitudinal measure lengthwise of the combustion chamber, andespecially a transverse opening or slit with a chordal width notexceeding .6 of the maximum inside diameter of the inner shell parallelto said chordal width, has been found to be the most desirable from thestandpoint of maintaining bivortical flow stability. A square air inletopening in the inner shell, and especially one having a maximumtransverse chordal width equal to a .6 of

the maximum inside diameter of the inner shell parallel to said width,has also been found desirable from the standpoint of maintaining stablebivortical flow conditions in the combustion chamber, but is not aseffective as the transverse slit or opening above described within acertain range of ratios between the flow through the annular coolingspace around the inner shell and the flow through the inlet air openingin said inner shell. The air inlet opening need not be an exactrectangle or an exact square but mayapproach these shapes; thus it maybe polygonal, elliptical or circular. However, whatever shape is chosenit should be designed as closely as possible to the criteria set forthfor the rectangular and square inlet openings if the same order ofresult is to be obtained.

It has also been found, in accordance with the present invention, thatby flattening the side of the inner shell opposite the air inletopening, and allowing the opposite side walls between said opening andthe flattened inner shell section to bulge outwardly, so that thedistance between these bulging walls is greater than the distancebetween the flattened inner shell section and the apertured section ofthe inner shell, the formation of the double vortex system isfacilitated, and the tendency towards the formation of or the mergenceof the two vortices into a single vortex is effectively minimized.

It has been found that a combustion unit constructed in accordance withthe present invention has an extremely high energy release rate. Forexample, while it has been diflicult at atmospheric pressure to obtainwith combustion units hitherto known an energy release rate of more aunit of the present invention, an energy release rate of 4,000,000 B. t.u. per cubic feet per hour at atmospheric pressure, and 20,000,000 B. t.u. per cubic feet per hour at p. s. i. has been obtained. Furthermore,these high energy release rates havebeen eifectively attained by meansof the present invention without undue complications in the structure ofthe unit, and with a minimum of destructive action thereon.

Various other objects, features and advantages of the invention will beapparent from the following particular description, and from aninspection of the accompanying drawings, in which:

Fig. l is an axial section somewhat diagrammatic of a combustion unitembodying the present invention;

Fig. 2 is a transverse section of the combustion unit takenapproximately along the line 2--2 of Fig. 1, and shown with parts brokenaway to reveal the structure behind these parts;

Fig. 3 is a transverse section of the inner shell or combustion chambertaken along the line 3-3 of Fig. l; and

Fig. 4 is a graph which shows flow stability transitional curvescorresponding to an air inlet opening of transverse rectangular shape inthe inner shell and to an inlet opening of square shape respectively,and indicating certain limiting conditions for maintaining bivorticalflow stability in said inner shell.

Referring to the drawings, the combustion unit is shown of the typewhich is particularly adaptable for use in connection with gas turbineplants. However, it must be understood that as far as certain aspects ofthe invention are concerned, the unit of the present invention may beadapted for other combustion uses where a high energy release rate isrequired.

The combustion unit of the present invention comprises a furnace orfirebox wall I, desirably in the form of a shell which is of metalresistant to heat, and which defines a combustion chamber H. Shell IDhas an intermediate section' lZ defining the burning out or secondarycombustion zone l3 of the combustion chamber II, and is closed at itsfront end by a head or nose-piece I4 defining therein the ignition zone[5. The rear or exhaust section I6 of the inner shell [0 is streamlinedand desirably of progressively reduced diameter downstream to affordexhaust gases of the required pressure and velocity at the outlet end ofthe unit. At its exhaust end, the shell I 0 may be connected to theinlet I! of a gas turbine or to any other conduit of the system orplant.

The inner shell I!) is enclosed in an outer protective metal shell l8which is concentric with and peripherally spaced from the inner shell IDby an annular space l9, serving as a flow passage for the cooling air,as will be described. The head end 20 of the outer shell 18 is desirablygenerally hemispherical. The rear section 2| of outer shell l8progressively decreases in diameter downstream until its neck snuglyembraces the throat of the inner shell l0, and to afiord ease ofassembly, desirably constitutes a separate unit attached to theintermediate outer shell section i8a by a flange bolt connection 22. Theinner shell I0 is supportably centered with respect to the outer shelll8 by this snug engagement between the two shells l0 and I8, and isfurther supported by spacers 49 therebetween, to be described.

l' or injecting fuel into the ignition zone II of the combustion chamberII, the head end 24 of the housing shell II has threaded or otherwisemounted thereon a fitting 23 connected to the outlet of a fuel injectionpump (not shown), and joined inside of said housing shell to a spraynozzle 24 projecting into the interior of said combustion chamber llthrough an opening 25 in the nose end l4 of the inner shell ll. Spraynozzle 24 is shown of the mechanical type which is adapted to projectand whirl liquid fuel under pressure into the interior of the chamber Hin the form of a hollow cone, and to atomize said fuel in said chamber.

For initiating the flame near the ignition zone I! of the combustionchamber H, there is fitted into the peripheral wall of the housing shellIt! a spark plug 26 projecting through an opening 21 in the top of theinner shell I4. and extending with its sparking end at a region near theouter margin of the conical fuel stream projected from the spray nozzle24. The spark plug 28 is desirably operated only sufliciently long toinitiate --ignition of the inflammable mixture in the ignition zone.Thereafter, primary combustion will continue without the aid of thespark plug.

The air for combustion is projected into the interior of the housingshell It by means of an air duct 30, shown in the general form of anelbow. Air duct 30 has its inlet end 3| disposed in front of the housingshell it with its center line of flow extending substantially parallelto the longitudinal axis or center line of the combustion chamber II. Aflange 32 is shown connected to the inlet end of the duct 30 forattachment to the outlet of an air compressor. The duct 30, which isstreamlined in the general direction of flow, and which is desirablyprovided at its bend with guiding baiiles 29 to afford smooth flowtherein, extends substantially for at least a portion thereof along thelength of the combustion unit, and has its discharge end 33 connectinginto a substantially circular opening 84 in the peripheral wall of theouter shell i8. Air duct 30 is desirably welded to the outer shell I 8to afford a light streamline construction especially adapted for use inconnection with aircraft, and is aerodynamically designed so that theair is delivered thereby into the interior of the housing shell i8 in adirection radially of the combustion chamber II, or at right angles tothe longitudinal axis of said chamber.

The air duct 30 is shown of the type especially useful in connectionwith modern axial flow compressors, which discharge compressed air atrelatively large velocity head. Duct 30 is therefore made with aprogressively increasing crosssection in the direction of flow in theform of a diffuser to recover a large part of the velocity head andconvert it into pressure head suitable for the conditions existing inthe combustion chamber. If the velocity head of the air at the inlet ofthe combustion chamber II is too great, then the pressure drop throughsaid chamber may also be comparatively large. Such large pressure dropsare undesirable, especially because of their adverse effect on theoverall efficiency of the system of which the combustion unit is a part.The air admitted into the combustion chamber ll must also have thenecessary velocity to produce the high combustion rate required, sincethere is a relationship between the combustion rate that can be obtainedand the velocity of the jet entering said combustion chamber through theopening 45 to be described.

The shape of the air duct it is shown of a specific design forapplication to a gas turbine layout proposed in connection, for example,with an aircraft installation. In such a power plant, all of theprincipal elements of the plant, as for example, the compressor, thecombustion unit and the gas turbine, would be arranged in line. In theparticular layout shown in the drawings. the compressor would bedisposed near the front of the combustion unit with its discharge endconnected to the duct inlet 3|, while the gas turbine would be disposedat the rear or exhaust end of the combustion unit with its inletconnected to the outlet l8 of the combustion chamber. There would be anumber of these combustion units circularly arranged around the axis ofthe turbine wheel.

For admitting combustion air from the duct 30 into the combustionchamber H, the inner combustion chamber shell Hi has an air inlet windowor opening 45 opposite to and centrally disposed with respect to theinlet air opening '34 in the wall of the housing shell l8, and havingits length and width smaller than the diameter of said air opening 34.The major part of the air from the duct 30 admitted into the interior ofthe housing shell l8 through its inlet 34 is directed substantiallyradially into the combustion chamber II, and as it hits the upper wallof said chamber, it is deflected thereby to form to similar adjoiningvortices having opposite senses of rotation, and completely filling thecombustion chamber ll almost to the exhaust end of the intermediateshell section I21. These reverse vortices advance continuously towardsthe discharge end of the combustion chamber II as the combustion processprogresses, while substantially maintaining in the intermediate sectionI! of said chamber their separate predetermined flow characteristics andtheir outer dimensions and form against transverse reduction or taper.

It has been found in accordance with the present invention, that inorder to create the double vortex pattern in the combustion chamber IIand to maintain this pattern substan-* tially stable, the air inletopening 45 should preferably be rectangular with its sides extendingsubstantially parallel to the longitudinal axis of the chamber, andshould have its measure lengthwise of said chamber no greater than itstransverse chordal dimension. It has also been determined that thetransverse chordal width of the opening 45 at right angles to thelongitudinal axis of the combustion chamber desirably should not exceed.6 of the maximum inside diameter of the inner shell parallel to saidchordal width, in order to maintain bivortical flow stability. The airinlet opening 45w should therefore be desirably in the form of atransverse slit or aperture having its transverse chordal measure atright angles to the longitudinal axis of the combustion chamber llgreater than its longitudinal measure lengthwise of said combustionchamber. A square opening 45 has a so been found desirable from thestandpoint of bivortical flow stability. Air in et opening 45 may alsoapproach a rectangle or square in shape and thus may be polygonal.elliptical or circular. However, in order to obtain the same order ofresults, such po y onal, elliptical or circular air inlet should bedesign d as closely as possible to the criteria set forth for therectangular and the square inlet openings It has also been determined inaccordance 7 with the present invention, that by elongating the crosssection of the inner shell III in a direction extending from oppositesides of the air inlet opening 45, the formation of the double vortexsystem is facilitated, and the tendency towards the formation ormergence of the two vortices into a single vortex is effectivelyminimized. More specifically, it has been found desirable to flatten theside of the inner shell H opposite the air inlet opening 45 and allowthe opposite side walls between said opening and the flattened innershell section to bulge outwardly as shown in Fig. 3. The inner shell.may be originally in cylindrical form, and may I air towards the frontend of the combustion chamber H. The primary combustion air projectedtowards the front end of the combustion chamber 1! through the openings48 assumes the form of a vortex ring extending around the infected fuelcone. Sufficient amount of the fuel from this cone is drawn and diffusedtowards the annular axis of the air vortex ring to form at said axis aninflammable mixture which is ignited by the spark plug 26. As theinflammable mixture is created along this vortex ring axis, it isignited, so that a pilot light is continuously afforded along said axis.

The nozzle 24, as already indicated, directs a metered quantity of fuelinto a fixed pattern of flow in a protected space whose volume isadusted according to the maximum capacity of fuel to be consumed. Therecirculating flow pattern which is maintained in the ignition spacereturns heat and so-called active centers from the stable flame into theairborne cloud of fluid drops in the chamber ll, thus maintainingcontinuous ignition.

As a result of the ensuing rapid intimate mixing of the air and fuel inthe head end of the combustion chamber ii, an intense ignition zone I5is created from which the flames are propagated along said chamber. Themixture propelled from the ignition zone l5 has an excess of fuel, andtends to be drawn towards and a ong the relatively low pressure centersof the two opposed vortices generated in the interior of the combustionchamber by the air admitted through its opening 45. As the axial columnsof fuel rich mixture advance along the combustion chamber ll, they aremixed rapidly and intimately with the encompassing cyclonic air, therebypropagating flames so intense as to burn themselves out almostcompletely before reaching the discharge end of the intermediate section12 of said chamber. Substantially complete combustion in the chamber IIis thereby assured.

As lon as the two reverse vortices in the comhustion chamber llsubstantially maintain their separate redetermined flow characteristics,no undesirable centrifugal separation of the fuel particles takes place.

A small portion of the air stream from the out let of the duct 30admitted into the housing I8 is diverted around and along the front ornose end 8 v l4 of the inner shell I II, to cool this sectlonof theshell without lowering the temperature of the gases in the chamber belowthe extinction temperature. Some of this diverted air cools the spraynozzle 24.

Part of the air stream directed into the interior of the housing l8 fromthe duct 30 is diverted around the inner shell in and towards thedischarge end of thecombustion unit to prevent destructive overheatingof the walls of said housing and the inner shell in. For that purpose,there is provided an intermediate shell 50 disposed between the innershell I!) and the outer housing shell I8, and acting as a shield forreducing heat radiation from the inner shell III to the outer housingshell l8. Intermediate shell 50 also serves to increase the surface bywhich transfer of heat is effected to the cooling air passing over saidintermediate shell, and is spaced from the two shells l0 and I8 to formtherewith two air cooling flow passages 5| open and communicating attheir front inletends 52 with the jacket space l9. For supporting andspacing intermediate shell 50 from the shells l0 and I8, suitablespacers 49 are provided desirably welded in position, in a manner whichwill afford ease of manufacture, ease of assembly and ease ofdiassembly.

For removably affixing the intermediate shell 50 in position between thetwo shells Ill and IS. the outlet end of said intermediate shell has aradially outwardly extending flange 53 clamped between the bolt flanges54 and 55 of the outer shell sections l8a and 2| respectively,constituting part of theflange bolt connection 22. Shell flange 53 has aseries of holes 56 to permit the cooling air from passage 5| to passtherethrough.

The cooling air streams from the annular flow flow passages 5| mergebeyond the flange bolt connection 22 in the single flow passage 51defined between the discharge sections l6 and 2| of the inner and outershells I0 and 18 respectively; the cooling air is desirably joined tothe exit gas stream from the combustion chamber 1 i by passing through aseries of holes 58 in the throat or neck of said discharge section [6.

It has been found that in order to obtain and maintain the substantiallypredetermined bivortical flow described, it is necessary to maintainthat proportion of the inlet air diverted rearwardly into the annularcooling passages 5| below a certain maximum. Hence, for any given formand size of inlet opening 45 only a limited portion of the total airsupplied may be permitted to flow into the cooling annular spaces 5|with out adversely affecting the stability of the double vortex flow insaid shell. If a greater amount is permitted to flow, instead ofproducing the double flame pattern characteristic of double vortex flow,a single vortex may be ultimately formed whose rotation changesperiodically from one sense to the other. This change may 00.- cur withrelatively high frequency.

Fig. 4 is a graph showing two flow stability transitional curves A andB, derived from an investigation of flow patterns in an isothermalsystem. Curve A corresponds to an air inlet transverse opening 45 whosetransverse dimension in a direction at right angles to the longitudinalaxis of the combustion chamber II is no more than .6 of the maximuminside diameter of the inner shell Ill before flattening, but is greaterthan its longitudinal dimension lengthwise of said chamber.

Curve 13 corresponds to a square air inlet trans verse opening 45 whosewidth is no more than .6 of the maximum inside diameter of the innershell I before flattening. The ordinate of the graph represents theratio of the flow through the annular spaces to the flow through theinner shell opening 45, while the abscissa represents thecross-sectional area of said opening. Tests were carried out, and thecurves A and B were plotted to indicate the demarcation between the zoneof stable double vortex flow and the zone of the unstable flow. To theleft and below each curve A or B, stable double vortex formation occurs.To the right and above each curve, flow instability occurs which-breaksdown the double vortex system.

It is apparent from the curves of Fig. 4, that for an air inlet openingof a definite size and shape of the general character described, thereis a maximum ratio between the flow through the annular spaces 5| aroundthe inner shell l0 and the flow through the air inlet opening, beyondwhich ratio unstable fiow conditions are encountered. As long as thisratio is maintained below this value, stable bivortical flow conditionsare created and maintained. For example, for an inlet opening arearepresenting about 13% of the cross-sectional area of the inner shell,the unit must be so proportioned that not more than .7 as much air flowsthrough the annular spaces 5| as enters the inner shell in a combustionchamber ll having a square inner shell air inlet opening.

By plotting conditions as indicated in Fig. 4, in an actual combustionset-up, the limiting ratio between the cross-sectional areas of theannular cooling spaces 5| to the cross-sectional area of the inner shellopening 45 to assure stable bivortical flow conditions in the combustionchamber I I, may be accurately determined.

In the operation of the combustion unit of the present invention, thesubstantially predetermined flow pattern is maintained at least alongthe intermediate section l2 of the combustion chamber II. The combustionof the gases is substantially completed by the time these gases reachthe discharge section l6 of the combustion chamber, so that thefiame'desirably does not extend beyond the inlet end of said section IS.

The combustion unit of the present invention can be made to effectivelyafford outlet temperatures ranging from 500 F. to 1800 F., required, asfor example, for certain efficient gas turbine operations, although byproper modification, within the teachings of this invention and byproper choice of materials out of which it is constructed, it can alsobe made to operate efficiently at temperaturesranging as low as 200 F.and as high as 3000 F. Also, the operation of the combustion unit of thepresent invention is stabilized because of the substantiallypredetermined flow and mixing conditions and patterns continuouslymaintained in the unit. This renders the unit susceptible to easyflexible control, allowing quick response to varying demands and closeregulation.

The combustion unit of the present invention permits stable operationover a wide range of fuel to air ratio for varying loads without thenecessity of adjusting the air flow. At the same time, the combustionunit avoids the deposition of soot and coke in the ignition zone, and iscapable of operation with large quantities of fuel and air over a widerange of load without smoking.

Furthermore, the unit of the present invention produces high rates ofcombustion, while requiring only a very small drop of pressure: of theair passing through the chamber. The unit, therefore, does not become adrag on the over-all elliciency of the plant system.

The unit of the present invention is especially suitable for use in gasturbine aggregates, It may also be used, however, for any application inwhich air is to be heated by burning finely divided fuel, such as liquidfuel in it, and it combines the advantages of compactness, cleanlinessof operation and small power requirements.

As far as certain aspects of the invention are concerned, the unit ofthe present invention may also be used without combustion, in caseswhere it is desired to concentrate a flowable medium along apredetermined zone of another flowable medium of lower density.

As many changes can be made in the above method and apparatus, and manyapparently widely different embodiments of this invention can be madewithout departing from the scope of the claims, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. An apparatus for operating on finely divided flowable material,comprising a wall defining an open chamber with an exhaust opening atone end, a housing wall enclosing said chamber wall and peripherallyspaced therefrom, and means for introducing a finely divided flowablematerial including a gaseous medium into said chamber and inducing itsflow unobstructed lengthwise of said chamber and towards said exhaustopening in the form of two adjoining vortices having" opposite senses ofrotation, said means comprising an inlet opening in the peripheralsection of said housing wall, an inlet opening in the peripheralintermediate body section of said chamber wall disposed between andspaced from the ends of said chamber wall and in approximate registrywith said first mentioned inlet opening, the space between theperipheral sections of said walls comprising a substantially annularpassage serving to connect said inlets, and means for radiallyintroducing said gaseous medium into the housing wall through its inletopening, said chamber wall inlet being of such size and shape I as tocause a part of said gaseous medium to be admitted into said chamber andto be directed by the wall thereof into the form of two adjoiningoppositely rotating vortices advancing unobstructed lengthwise of saidchamber towards its exhaust opening.

2. An apparatus as described in claim 1, in which theinlet opening ofsaid chamber wall has its length along said chamber no greater than itswidth transverse to the length of said chamber.

3. An apparatus as described in claim 1, in which the inlet opening ofsaid chamber wall approximates a rectangular form which has some of itssides substantially parallel to the longitudinal axis of the chamber,and has its measure along said chamber substantially less than itsmeasure transverse to the length of said chamber.

4. An apparatus as described in claim 1, in which the inlet opening ofsaid chamber wall is substantially square with two sides substantiallyparallel to the longitudinal axis of the chamber.

5. An apparatus as described in claim 1, in which the inlet opening ofsaid chamber is substantially rectangular with two sides substantial- 1!1y parallel to the longitudinal axis of the chamber, has its lengthalong said chamber no greater than its chordal width transverse to thelength of said chamber, and has its chordal transverse width no greaterthan .6 of the maximum inside width of said chamber parallel to thedirection of said chordal transverse width.

6. An apparatus as described in claim 1, comprising a supply ductconnected to the inlet opening of said housing wall and extending for asubstantial portion of its length in the same general longitudinaldirection as said housing wall.

7. In a combustion unit, the combination comprising a wall forming anopen combustion chamber and defining in said chamber an ignition zoneand a burning-out zone for flame propagation lengthwise of said chamber,a housing wall enclosing said chamber Wall and peripherally spacedtherefrom, means for introducing a stream of finely divided fuel intosaid ignition zone, means for directing primary combustion air into saidignition zone to form an inflammable mixture in said zone, and means forcreating two combustion air streams in said chamber in the form of twoadjoining oppositely rotating vortices and advancing them unobstructedtowards the exhaust end of said chamber, said last-mentioned meanscomprising an air inlet opening in the peripheral section of saidhousing wall disposed between and spaced from its ends, and an air inletopening in the intermediate peripheral body section of said chamber walldisposed between and spaced from the ends of said chamber and inapproximate registry with said first mentioned inlet opening, the spacebetween the peripheral sections of said walls comprising a substantiallyannular passage serving to connect said air inlets whereby a part of theair stream entering said housing is admitted radially into said chamberthrough its inlet opening and is directed by the chamber wall into theform of two adjoining oppositely rotating vortices.

8. The combination as described in claim 7, in which the inlet openingof said chamber wall has its length along said chamber no greater thanits width transverse to the length of said chamber. I

9. The combination as described in claim 7, in which the inlet openingof said chamber wall approximates the rectangular form with some of itssides substantially parallel to the longitudinal axis of the chamber,and has its measure along said chamber substantially less than itsmeasure transverse to the length of said chamber.

10. The combination as described in claim '7, in which the inlet openingof said chamber wall is substantially square with two sidessubstantially parallel to the longitudinal axis of the chamber.

11. The combination as described in claim 7, in which the inlet openingof said chamber is substantially rectangular with two sidessubstantially parallel to the longitudinal axis of the chamber, has itslength along said chamber no greater than its chordal width transverseto the length of said chamber, and has its chordal transverse width nogreater than .6 of the maximum inside width of said chamber parallel tothe direction of said chordal transverse width. 1

12. The combination as described in claim '7, in which the transverseregion of said chamber wall containing its inlet opening is elongated atthesides of said latter opening, whereby the maximum distance betweenthe sides of said chamber wall is greater than the maximum distancebetween said latter opening and the section of said chamber walldiametrically opposite to said latter opening.

13. The combination as described in claim '7, in which the transverseregion of said chamber wall containing its inlet opening is shaped fromcylindrical form with the section of said chamber wall diametricallyopposite said latter opening flattened, and the sections of said chamberwall on opposite sides of said flattened section bulged outwardly.

14. The combination as described in claim 7, in which the transverseregion of said chamber wall containing its inlet opening is shaped fromcylindrical form with the section of said chamber wall diametricallyopposite said latter opening flattened and the sections of said chamberwall on opposite sides of said flattened section bulged outwardly, andin which the inlet opening of said chamber wall approximates therectangular form with some of its sides substantially parallel to thelongitudinal axis of the chamber, has its length along said chamber nogreater than its chordal width transverse to the length of said chamber,and has its chordal transverse width no greater than .6 of the maximuminside width of said chamber parallel to the direction of said chordaltransverse width.

15. In a combustion unit, the combination comprising a wall forming anopen combustion chamber and defining in said chamber an ignition zoneand a burning-out zone for flame propagation lengthwise of said chamber,a housing wall enclosing said chamber wall and peripherally spacedtherefrom, means for introducing a stream of finely divided fuel intosaid ignition zone, means for directing primary combustion air into saidignition zone to form an inflammable mixture in said zone, and means forcreating two combustion air streams in said chamber in the form of twoadjoining oppositely rotating vortices and advancing them unobstructedtowards the exhaust end of said chamber, said last-mentioned meanscomprising an air inlet opening in the peripheral section of saidhousing wall disposed between and spaced from its ends, and an air inletopening in the intermediate peripheral body section of said chamber walldisposed between and spaced from the ends of said chamber and inapproximate registry with and communicating with said inlet housing wallopening through the spacing between the peripheral sections of saidwalls, whereby the air stream admitted radially into said chamberthrough its inlet opening is directed by the chamber wall into the formof two adjoining oppositely rotating vortices, the portion of thehousing wall between its air inlet opening and the exhaust end of saidcombustion chamber forming with said chamber wall an annular passagecommunicating at one end with said latter opening, whereby part of theair admitted through said latter opening is diverted to said passage forair cooling the housing wall, said annular passage being of suchdimensions at its inlet end as not to disturb the predetermined doublevortex-forming characteristics of the incoming air, whereby thepredetermined bivortical flow pattern of the air in said combustionchamber is continuously stably maintained dur-'- ing combustionoperations.

16. In a combustion unit, the combination comprising a wall forming anopen combustion chamber and defining in said chamber an ignition zoneand a burning-out zone for flame propagation lengthwise of said chamber,a housing wall enclosing said chamber wall and peripherally spacedtherefrom, means for introducing a stream of finely divided fuel intosaid ignition zone, means for directing primary combustion air into saidignition zone to form an inflammable mixture in said zone, and means forcreating two combustion air streams in said chamber in the form of twoadjoining oppositely rotating vortices and advancing them unobstructedtowards the exhaust end of said'chamber, said lastmentioned meanscomprising an air inlet opening in the peripheral section of saidhousing wall disposed between and spaced from its ends, and an air inletopening in the intermediate peripheral body section of said chamber walldisposed between and spaced from the ends of said chamber and inapproximate registry with and communicating with said inlet housing wallopening through the spacing between the peripheral sections of saidwalls, where'-y the air stream admitted radially into said chamberthrough its inlet opening is directed by the chamber wall into the iormof two adjoining oppositely rotating vortices, the portion of thehousing wall between is air inlet opening and the exhaust end of saidcombustion chamber forming with said chamber wall an annular passagecommunicating at one end with said inlet opening, whereby part of theair admitted through said inlet opening is diverted to said passage forair cooling the housing wall, the ratio of the cross-sectional area ofthe annular passage to the cross-sectional area of the air inlet openingin said chamber wall being within the doublevortex stability zone ofoperation of the combustion unit, as determined by a graphicrepresentation of the limiting bivortical flow stability characteristicsof the unit. 1

17. In a combustion unit, the combination comprisin a combustionchamber, at least part of which is formed by a chamber wall defining anignition zone from which the flame i propagated lengthwise of saidchamber towards its exhaust end, said chamber wall having a combustionair inlet opening, a housing wall around said chamber wall peripherallyspaced therefrom and having an inlet openin in its peripheral sectioncommunicating with said chamber wall inlet opening, said housing wallbeing of jacketed construction fora section of its length to define anannular cooling passage extending from the inlet opening of said housingwall to the exhaust end of said combustion chamber, said cooling passagecommunicating at one end with said latter inlet opening, whereby aportion of the air admitted through said latter opening into saidchamber is diverted through said passage for cooling the housing wall,means for injecting a stream of finely divided fuel into said ignitionzone, means for directing a stream of primary combustion air into saidzone, and duct means for delivering air to said housing wall inletopening and into said combustion chamber, said combustion chamber beingadapted to deflect the air admitted therein through said housing wallinlet opening into two adjoining oppositely rote ting vortices ofsubstantially predetermined floz'. pattern, and said cooling passagebeing of such dimensions at its inlet end as least to disturb thepredetermined vortexforming characteristics of the air admitted fromsaid duct means whereby the predeterminedbivortical flow pattern of theair in said combustion chamber is continuously maintained duringcombustion operations.

18. An apparatus as described in claim 1, in which an intermediate shellis located in the annular passage downstream beyond the air inletsserving as a'radiation shield for the outer shell.

MARTIN A. MAYERS. HANS T. HOLZWARTH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 781,308 Smith 1 Jan. 21, 19052,110,209 Engels a Mar. 8, 1938 2,353,929 Ray July 18, 1944 2,398,654Lubbock Apr. 16, 1946 2,420,135 Hennig May 6, 1947

